Organic light-emitting diode (OLED) displaying is being widely researched by people in recent years due to its advantages of high brightness, high light-emitting efficiency, wide angle of view, low power consumption, etc., and is rapidly applied to the new generation of display. The driving modes of OLED displaying can be divided into two modes, passive matrix OLED (PMOLED) and active matrix OLED (AMOLED). Though the cost of PMOLED is a low, high-resolution display can not be achieved due to crosstalk. Moreover, PMOLED has a large driving current, and therefore the service life of OLED is reduced. In contrast, in AMOLED, numbers of transistors which serve as current sources are included at individual pixels, so that crosstalk is avoided. The required driving current is smaller and power consumption is lower so that the service life of OLED is prolonged and a high-resolution display can be realized.
A pixel circuit of traditional AMOLED has a simple structure of two thin film transistors (TFT). Though such a circuit is simple in structure, the shift of threshold voltages of driving transistor T1 and OLED or non-uniformity the threshold voltages of TFT devices at various positions of panel caused by the fact that the TFT devices are made of polycrystalline materials cannot be compensated. When there is shift of threshold voltages of transistor T1 or the threshold voltages are inconsistent at various positions of the panel, the driving current IDS may change, and different pixels on the panel may also have different amount of shift due to different biasing voltages, which may cause non-uniformity of panel display.
Currently, the driving modes of pixel circuit mainly include two modes, one is progressive scanning, and the other is simultaneous compensation and emission of light.
For progressive scanning mode, in one frame, the pixel circuits of each line are driven in sequence respectively, as shown in FIG. 1; the driving process of each line comprises an initialization phase, a threshold compensation phase, a programming phase and a light emitting phase. After the pixels of each line have finished programming, the process immediately proceeds to the light emitting phase. Herein, the initialization phase and the threshold compensation phase are referred to as the compensation phase for short. On the whole, the time of one frame is partially used for compensation and partially used for emitting light, and the whole one frame time is used for light emitting. In this driving mode, for the pixels of each line, the time of compensation and programming is short and the time of light emitting is long, but the pixel circuit of each line requires an independent control line, and the gate driving circuit is relatively complicated.
For the mode of simultaneous compensation and emission of light, in one frame, the driving process of each line comprises an initialization phase, a threshold compensation phase, a programming phase and a light emitting phase. Unlike the traditional progressive scanning, all the pixels are compensated altogether, and then the pixels of each line are programmed in sequence. After the pixels of all the lines have finished programming, they emit light simultaneously, as shown in FIG. 2. Herein, the initialization phase and the threshold compensation phase are referred to as the compensation phase for short. On the whole, the time of one frame is partially used for compensation and partially used for light emitting, and the time of light emitting is short. In this driving mode, the control lines of all the pixel circuits on the panel are shared in common (i.e., global control lines are used). However, since there is much idle waiting time for each line during the programming phase, the overall programming time is long and the time of light emitting is short.